Question

Which of the following situations requires no net force? A moon orbiting around a planet. An elevator moving down with a constant speed of 2 m/s A skateboarder who slows from 10 m/s to 5 m/s. A pendulum swinging back and forth.

Answer 1

Explantion:

A moon orbiting around a planet - Here requires Centripetal Force and Gravitational Force.

A skateboarder who slows from 10 m/s to 5 m/s - Here requires Frictional Force to slow from 10 m/s to 5 m/s

A pendulum swinging back and forth - A pendulum is an object hung from a fixed point that swings back and forth under the action of gravity.... when the swing is raised and released , it will move freely back and forth due to the force of gravity on it. So here gravitational force is required.

An elevator moving down with a constant speed of 2 m/s - Newtons First law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. So Here requires no Force, because elevator moving down with a constant speed of 2 m/s